1. Field of the Invention
This invention relates to a shield wire for power supply to an apparatus and, in particular, to a shield wire for power supply to various apparatuses of an automobile.
2. Description of the Related Art
The shield wire has, outside of a covered conductor, a braided shield which is made of copper wire, tin-plated copper wire etc. with a diameter of tens to hundreds of μm. The braided shield is connected to a metallic connector at its ends, and the metallic connector is grounded, whereby shielding effect can be obtained to prevent malfunction caused by electromagnetic wave etc.
Recently, in automobiles, hybrid cars prevail and its electrical apparatuses come into wide use. Further, shield wires for various apparatuses of the automobile are used at a high voltage and large current. Thus, accordingly, as the hybrid cars prevail and the electrical apparatuses come into wide use, the number of required wiring materials (shield wires) increases. Thereupon, the shield wire needs to be easily bent to save space where they are installed.
FIG. 1 is a plain view showing a conventional shield wire. As shown, the shield wire 350 has connection terminals 356, 356 clamped at its ends, and clamp marks 356a are formed at the clamp portion.
FIG. 2 is a cross sectional view cut along a line a-a in FIG. 1. As shown, the shield wire 350 has, on the periphery of a conductor 357, an insulation 355, a braided shield 352, and a cover layer (insulation) 351, in this sequence from the inside out.
FIG. 3 is a cross sectional view cut along a line b-b in FIG. 1. As shown, the cover layer 351 is peeled at the ends, the braided shield 352 is folded back, and a clamp ring 353 is provided on the folded portion of the braided shield 352. A shield connector 354 is provided on the folded-back base (i.e., the boundary between the braided shield 352 and the insulation 355) of the braided shield 352. The shield connector 354 has a screw-connected terminal (not shown) for grounding.
FIG. 4 is a plain view showing a conventional shield wire unit. The shield wire unit 380 for connecting the shield wire and a transmission-side feeder housing is composed of plural (six in FIG. 4) shield wires 350 and a plastic housing 381. The housing 381 is composed of a frame member 382 with a bottom 382a and a housing cover 383 to cover the upper face of the frame member 382. The housing cover 383 is fixed through fixing screws 384 to the frame member 382. Recently, the frame member can be made of a metallic shield case (e.g., JP-A-2002-208456).
The frame member 382 is provided with plural openings at its sidewall. The shield wire 350 is inserted through the opening in the housing 381. Between the shield wire 350 and the opening, a waterproof cover 358 is provided to prevent the penetration of water from outside. The bottom 382a of the frame member 382 is made of an insulating material. Terminal bases 386 and ground terminal bases 387 are mounted on the bottom 382a. Although not shown, the terminal base 386 is provided with a wiring to supply current to the transmission, and the ground terminal base 387 is grounded externally.
The connection terminal 356 of the shield wire 350 is screw-connected through a washer 388 and a bolt 389 to the terminal base 386. The shield connector 354 of the shield wire 350 is screw-connected through a bolt 390 to the ground terminal base 387.
FIG. 5 is a schematic diagram showing a connection state of the conventional shield wire unit. As shown, the shield wire unit 380 is arranged such that the shield wire is connected to an inverter housing 481 on the side of the shield connector 354 (on the left side in FIG. 5), and the plural shield wires 350 are bundled and aligned through a fixing guide member 482.
However, the conventional shield wire 350 is not good in its bending property since it uses a heat-resistant resin as the insulation 355 and the entire thereof is covered with the braided shield 352. Thus, in the case of attaching the shield wire 350 to a body etc. of a car, it is difficult to bend the shield wire 350 along the shape of the attaching part. As such, it has a problem in its handling property when it is attached.
Further, when the shield connector 354 needs to be attached to the ground terminal base 387 after attaching the shield wire 350 to a predetermined location of the housing 381, the efficiency of the attaching work is not good.
Further, depending on the position where the shield wire 350 is attached, the shield wire 350 may be hit by mud or gravels and the cover layer 351 may be broken thereby.
On the other hand, when the shield wire 350 is attached near the engine of the car, it may be subjected to vibration and heat thereof. If it exceeds the limit of heat resistance, the cover layer 351 may crack and the braided shield 352 may erode or disconnect. As a result, the shield effect thereof will lower. Therefore, the cover layer 351 needs to have such a strong structure or material that can endure the vibration and heat. Especially when the shield wire is connected to the feeder housing on the transmission side, large current needs to pass through it. The braided shield 352 for the shielding is also subjected to current flow. Therefore, the braided shield 352 may generate heat, and resistivity may increase at the connection part between the feeder housing and the shield wire. Further, due to the heat generated by the braided shield 352, the cover layer 351 may crack.